The present invention relates to an improvement in a retainer such as is conventionally used to secure a tool such as a punch, or, a die bushing (or die or die button), or forming tool, removably in a die shoe.
A retainer for a punch (punch retainer) secures the punch held within it to a die shoe, usually the upper, of a punch press so that the punch may be moved downwards into a die bushing with precision, over and over again so that stringent specifications of a punched sheet may be maintained. The die bushing, in turn, is held in a retainer (die bushing retainer) and secured to an opposed die shoe of the punch press. Typically both the retainers are removably secured to their respective die shoes; and the punch and the die bushing are also removably secured in their respective retainers.
For several decades a xe2x80x9cball lock punch retainerxe2x80x9d has been used to secure the punch, and in fewer instances, also the die bushing which is more often clamped to the lower die shoe of the press, or tightly fitted into a recess therein. Despite the many problems associated with the use of a spring-biased retaining ball biased against a helical spring held in an angulated elongated, passage within the retainer, this is the industrially favored mechanism because of the relatively low cost of manufacturing its components. However, aside from the relatively poor precision with which the shank (upper portion) of such a punch can be positioned, and the tolerable accuracy with which the point (lower portion) of the punch makes a through-passage (xe2x80x9cholexe2x80x9d for brevity) of arbitrary cross-section in a sheet of stock being punched, a serious problem is that it is routinely an arduous and frustrating task to release a punch when it is to be replaced. One of the reasons is that repeated operation of the punch distorts the shape of the ball, which then becomes immovably lodged against the punch or against a helical spring against which the ball is biased. The problem of replacing the punch is worse when the ball is sheared, which typically happens when the stripping force (during withdrawal of the punch from the stock) exceeds that which the ball can withstand. In operation, punches are routinely subjected to unexpectedly large stripping forces typically cause by galling of the point.
An inherent result of using a ball seat or pocket in the shank of a punch to lock it with a ball is that, the shank of the punch is of necessity, cylindrical. If the point of the punch is non-circular in lateral cross-section, it can be sharpened only until the point is used up and the shank is reached. Moreover, by reason of the clearances required between the pocket and the ball, and the relatively small force exerted by the spring against the ball, it is difficult to maintain concentricity with tolerance less than 0.001 inch (0.0254 mm). Particularly when the shape of the hole to be punched is other than circular, the shank is not held tightly and non-rotatably in its elongated passage with the result that the play between the ball and the pocket results in slight but unacceptable variations in orientation of the hole punched. These problems are more readily envisioned by reference to FIGS. 1 and 2 in which the prior art mechanism is briefly described. Moreover, the structural differences and their effect on the forces exerted on a tool to be replaced, when compared to those of the present invention, will more readily be appreciated.
Similar considerations apply to securing a forming tool which operates in a forming press and which forming tool is typically secured in a manner analogous to a punch. A commonly used forming punch has a point for making the desired hole in a sheet of stock, and has an upwardly flared conical portion directly above the tip of the point. The flared portion serves to provide desired concavity. Hereafter, for brevity and convenience, a punch and a forming tool or forming punch, and a die bushing are together referred to by the term xe2x80x9ctoolxe2x80x9d; and are identified individually when specifically referred to.
Referring to FIGS. 1 and 2, there is illustrated a retainer block indicated generally by reference numeral 10 and a conventional punch 20 held therein. A forming tool, if used, would be analogously held. The retainer block 10 includes a through-hardened backing plate 12 conforming to the upper surface of the retainer block, both being adapted to be secured to an upper die shoe of a punch press or other machine with a punching or forming function by suitable fastening means such as Allen-head screws (not shown). Since a tool (punch or forming) is generally used in a vertical attitude in a punch or forming press, the description herein refers to upper and lower in relation to such attitude. The retainer block 10 is provided with a cylindrical bore or tool socket 14 in which is slidably inserted and removably secured the shank (upper portion) 22 of the punch 20, the lower portion of which is an oval-shaped point 24. Block 10 is also provided with a cylindrical bore 15 which is angularly disposed relative to the bore 14 and which extends inwardly and downwardly into the retainer block 10 so as to partially intersect socket 14. The partial intersection occurs because the lower end of the bore 15 is provided with a stepped surface forming ball seat 13.
A retainer ball 16 is movably disposed in bore 15, and a helical compression spring 18 is snugly held in the bore 15 with one end abutting the backing plate 12 so as to urge the ball 16 outwardly of the intersecting portion of bore 15. Though the ball projects into the socket 14 the ball cannot escape (into the socket 14). The retainer block is also provided with a through-passage or release-hole 17 through which a thin rod or drift pin is inserted to push the ball upward and move it out of the ball seat 13 when the punch 20 is to be removed. To replace the ball 16 when it gets distorted or damaged, the retainer block 10 is removed from the backing plate 12 and the spring and ball removed through the top of bore 15.
The shank 22 is provided with a semi-pocket or ball seat 25 shaped generally like a one-half of a falling tear drop viewed in longitudinal elevation, and which is adapted to receive locking ball 16 to releasably lock the punch 20 in the bore 14. The pocket""s upper portion 26 appears as a straight section forming a continuation of the bore 15; and the lower portion is provided with a return section 28 which is curved upon a radius greater than the radius of the ball 16 so as to connect the deepest part of the pocket 25 to the surface of the shank. When the ball 16 is held in pocket 25 its bottom may be in contact with the ball if the radius of section 28 is substantially greater than that of the ball; or, if the radius of the ball is substantially greater than that of the return section 28, the extreme edges 34, 35 of the pocket 25 will contact the ball.
To appreciate the advantage of locking a punch precisely positioned in the retainer block, the problem with using a pocket and retaining ball is illustratively presented in FIGS. 3 and 4 so it may be more readily visualized. Both problems, namely of securing the tool to the die shoe, and positioning the punch (and die bushing) precisely, is particularly severe with relatively small diameter punches having a shank less than about 7.6 cm (3 ins.) in diameter. A larger diameter shank may be secured and precisely positioned with screws and dowels through the shank and die shoe. In FIG. 3 is shown a shank 22A having a pocket 25A with an arcuate section having a radius substantially greater than that of ball 16A, allowing the punch to rotate slightly in either direction, as shown by the arcuate double-headed arrow, so that accurate alignment between a non-circular punch and its corresponding die bushing cannot be maintained. In FIG. 4, in shank 22B, the arcuate section of pocket 25B has a radius smaller than that of a ball 16B so that it engages the corner portions 34B, 35B of the pocket in the shank. Under operating conditions which generate high forces, depending upon the relative hardness of the ball and the shank, either one or the other, or both are distorted or damaged; at the very least the extreme edges 34, 35 of the pocket are pushed outward as shown at 38, 39.
Thus for optimum locking it is desirable to have the diameter of the ball accurately adapted to fit in the pocket so as to have the pocket contact the ball at two opposed points 33 inwardly spaced apart from the edges 34, 35 as shown in FIG. 2, the distance inward being chosen so as to avoid forcing the extreme edges 34, 35 outwards. Such precision is difficult to achieve in practice, and is proportionately so expensive as to be uneconomical. When achieved it will be evident that, the ball being a sphere, the contact at 33 is essentially point-contact with the surface of the pocket 25 and not substantially different from the point contact between the ball 16B and shank 22B with the pocket 25B.
To avoid using a ball lock mechanism, wedges have been used to lock a punch transversely in a retainer as illustrated in U.S. Pat. No. 3,137,193, the shank is provided with a flat (shank flat) on one side thereof which flat engages a cooperating flat formed on a tapered retaining pin fitting within a transversely extending opening formed in the punch retainer. Since the tapered pin cannot prevent the punch from moving vertically the shank must also be held by a pin the inner end of which has a sloping wedge surface which is adapted to engage a cooperating wedge surface formed on the shank of the punch as a part of a cutout on the opposite side from the shank flat. Even if one accorded this means for holding a punch in a retainer great merit for accuracy, it is evident that such a punch and retainer function to wedge the shank laterally, not vertically. The inclined surfaces form acute angles with the horizontal in a horizontal plane, that is, xe2x80x9claterally acutexe2x80x9d; not with the vertical in the vertical plane, that is xe2x80x9cvertically acutexe2x80x9d. Moreover such a mechanism is complicated and expensive to produce. Equally evident is why the ball lock punch retainer is the current standard for the machine tool industry.
In an analogous manner, when it is inconvenient or impractical to clamp a die bushing in a die-receiving hole, or one seeks either to avoid press-fitting a die bushing in the die-receiving hole, or using a ball lock mechanism to do so, the die bushing may be held as shown in U.S. Pat. No. 3,535,967 to Whistler et al. The die bushing is accurately positioned in a flexible retainer into which it is press-fitted and is held in the die retainer block by providing one side of the bushing with a flat surface, the flat cooperating with a corresponding flat on an aligning pin disposed transversely within a. transversely extending opening in the die retainer.
European Patent 0 446 536 A1 to Guy Pignon discloses several embodiments of an invention, including an upside-down perspective view of an assembly, illustrated in FIG. 19 of a pair of complementary wedges 1 and 2 forming a parallelpiped, and another assembly, in a normal operating position, illustrated in cross-sectional view in FIG. 20, of a single wedge 1, each of which assemblies secures a punch C held in a support plate (or retainer block) 6 which in turn, is secured to a support block (or die shoe) 7 through a backing plate 3. In each instance, the screw 5 enters the die shoe 7; in FIG. 20 the screw 5 is inserted through the die shoe 7 and threadedly secured in the wedge 1; in FIG. 19 the screw 5 is inserted through the retainer block 6 and threadedly secured in the die shoe 7 (shown in FIG. 2 of the Pignon reference).
In each embodiment of the Pignon assembly, the movable wedge 1 is directly, threadedly attached to the die shoe and provides a vertical tool-mating surface against which the tool (punch C) is clamped, and in each case, the orientation of the wedge is vertical, that is, in a substantially inverted V-shaped attitude in which the tool-mating surface is vertical and the opposed surface forms a vertically acute angle, downwardly directed away from vertical, the opposed wedge surface being in contact with the correspondingly inclined surface of the retainer block 6.
In this substantially inverted V-shaped attitude it is evident that the active wedging function is provided only during downward operation of the punch, by virtue of the angled wedge surface. By xe2x80x9cactive wedging functionxe2x80x9d is meant that there is positive mechanical interference, as if functioning as a detent, by virtue of the angled surface impeding movement in the direction in which the forming tool is moving, whether the forming tool is driven through the stock or withdrawn from it (stripped). In the ""536 reference, when the punch has punched out the desired shape from the stock, and is then withdrawn, there is no active wedging function because the stripping forces are directed along the vertical tool-mating and shank surfaces (providing no active wedging function, only a clamping function); the inclined surface of the wedge which can now slide out because of the downward and outward inclination of the angle of the wedge surface. The same problem, namely providing only a clamping function and no active wedging function, arises with the complementary wedges in FIG. 19. Thus the wedging function provided by the Pignon assemblies is only useful in relatively light duty punching applications where the stripping force is low enough so as not to loosen the clamped punch during its retraction through the stock. This clamping function is more clearly evident in FIGS. 6 and 7 of the ""536 reference.
During operation, because of the high forces generated during punching out steel and other metal stock, any wedge with a tool-mating surface becomes tightly held in the wedge cavity. To replace a punch, the wedge must be loosened in its cavity. To do this in the assembly shown in FIG. 20, access through the die shoe is necessary. The die shoe must be lowered out of the press, the screw 5 removed, and the wedge 1 driven downward with a dowel inserted through the bore of the screw. In FIG. 2 of the ""536 reference, there is no access through the die shoe and how the wedge may be loosened is not described.
Note that, in each embodiment of the Pignon assembly, the screw which secures the wedge in the reatiner block 6, is either threaded into the die shoe 7 or is slidably inserted though it, to directly attach the wedge to the die shoe. In each instance, assembly requires removing the die shoe from the punch press and then refitting the die shoe in the press. Even in a relatively small 90-ton punch press, a typical die shoe which is about 61 cmxc3x9776 cmxc3x975 cm (24xe2x80x3xc3x9730xe2x80x3xc3x972xe2x80x3) weighs about 200 Kg (440 lb) or more; removal requires use of a fork-lift truck or overhead crane. Moreover, every time the location of the wedges are changed, as when a different shape is to be punch out with a different punch, the die shoe must be machined for the new locations of threaded bores or through-passages, with attendant problems of new locations partially overlapping old, and in any all instances, limiting the useful life of a die shoe.
The problems of using a wedge which is attached to the upper die shoe and provides only a clamping function during stripping, and of having to remove and machine the die shoe from the press to install an assembly, are both overcome by the invention described herein. It accomplishes what the ball lock does, and much more, not only with respect to precision and strength, but also for economy and ease of operation; and permits quick replacement of the tool by releasing it in its tool-receiving cavity with a force which is proportional to the pitch of threads in the screw means which secures the wedge in its wedge cavity to the backing plate of the retainer block.
It has been discovered that a tapered holding means such as a wedge-shaped block (xe2x80x9cwedgexe2x80x9d) locks a forming tool such as a punch or a die bushing and locates it accurately in a retainer block secured to a backing plate of a punch press without being directly attached to the upper die shoe; though the wedge is tightly locked in the retainer block during operation, the forming tool may be replaced without access through the upper die shoe or disassembling the retainer block; preferably, biasing means allows the wedge to lock the forming tool to provide an active wedging function.
It is therefore a general object of this invention to provide a tooling construction comprising in combination, a retainer block, forming tool such as a punch, die bushing, and a wedge means directly attached to the backing plate but not directly attached to the die shoe of a punch press; the retainer block has a tool-and-wedge-receiving cavity or passage therein adapted to receive both the punch or die bushing and the wedge means which, in operation, are locked in position relative to each other; the wedge means is provided with at least one inclined surface inclined from the vertical, and a tool-contacting, preferably tool-mating surface; and, biasing means to releasably secure the wedge within the retainer block so as to lock and unlock the punch in the tool cavity.
It is a specific object of this invention to provide a substantially inverted V-shaped wedge directly attached to the backing plate but not directly attached to the upper die shoe, and releasably movably secured in a wedge cavity in a retainer block, the wedge having one vertical tool-mating surface and an opposed surface in contact with a retainer block, the opposed surface forming a vertically acute angle surface directed downward and away from the vertical (see FIGS. 6 and 7).
It is another specific object of this invention to provide a substantially V-shaped wedge directly attached to the backing plate but not directly attached to the upper die shoe, and releasably movably secured in a wedge cavity in a retainer block, the wedge having one vertical surface and an opposed surface forming a vertically acute angle (measured from the vertical), the inclined surface providing a detent function by interfering with removal of the punch by stripping forces (see FIGS. 8, 9, 10).
It is another specific object of this invention to provide a substantially V-shaped wedge directly attached to the backing plate but not directly attached to the upper die shoe, and releasably movably secured in a wedge cavity in a retainer block, the wedge having opposed oppositely inclined surfaces diverging from the vertical, forming vertically acute angles measure from the upper vertical line (see FIGS. 15, 15A, 17 and 18).
It is another specific object of this invention to provide a generally inverted V-shaped wedge directly attached to the backing plate but not directly attached to the upper die shoe, and releasably movably secured in a wedge cavity in a retainer block, the wedge having opposed surfaces each forming a downwardly vertical acute angle (measured on each side of the vertical in the lower quadrants); the angles may be oppositely directed to provide diverging wedge surfaces (see FIG. 11), or similarly directed to provide non-diverging wedging surfaces (see FIGS. 15C, 15D, 17A, 18A).
It is also a general object of this invention to provide a method for securing a punch or forming punch or die bushing (xe2x80x9ctoolxe2x80x9d) in a retainer block, comprising, forming therein a tool-and-wedge-receiving cavity shaped to provide both a tool cavity and a wedge cavity into each of which is closely received the tool and the wedge respectively; forming a wedge means adapted to be inserted in the wedge cavity, the wedge having an inclined surface (xe2x80x9cwedge-inclined surfacexe2x80x9d); shaping the wedge to provide both a tool-mating surface and the wedge-inclined surface for contact with the retainer block, each surface preferably oppositely disposed relative to the other; assembling the wedge and the retainer block so as to form a tool cavity without directly attaching the wedge to the upper die shoe of the punch press; inserting the tool within the cavity so as to be closely received therein and slidable relative to the tool-mating surface; and, providing relative movement between the tool-mating surface and the tool, sufficient to releasably lock the tool in the cavity.
It is a specific object to provide corresponding inclined surfaces on the following cooperating surfaces: (i) the wedge-inclined surface and a wall of the cavity in contact with the wedge inclined surface (see FIGS. 6-9, 15); (ii) the tool surface and the wedge""s tool-mating surface (see FIG. 10); or (iii), both (i) and (ii) (see FIGS. 11, 17 and 18).
It is a specific object of this invention to provide a method for securing and releasing a punch or forming tool in a retainer block, comprising, forming a wedge-shaped cavity in the block wherein at least one surface of the block (xe2x80x9cinclined block surfacexe2x80x9d) is inclined from the vertical; forming a single wedge having at least one inclined surface (xe2x80x9cwedge inclined surfacexe2x80x9d) adapted to slidably cooperate with a correspondingly inclined surface on either the block or the punch, or both, the wedge being shaped to provide a tool-mating surface and a wedging surface, one oppositely disposed and inclined relative to the other, when the wedge is inserted into the wedge cavity, the tool-mating surface in cooperation with surfaces of the wedge cavity providing a tool passage within which the tool is to be held; inserting the wedge into the cavity; inserting the tool into the tool passage; and releasably securing the wedge within the retainer block to permit vertical movement thereof relative to the retainer block without directly attaching the sedge to the upper die shoe of the press.
It is another general object of this invention to provide a method for making a retainer block and a tool adapted to be held in a cavity therein, comprising positioning a block of material in a wire electric discharge machine (xe2x80x9cEDMxe2x80x9d); programming the machine to cut a tool of desired shaped from within the block with a wire so as to form a tool cavity having an arbitrary cross-section and being open at both the top and bottom of the block; and, programming the machine to cut a wedge of desired shape from within the retainer block with the wire, the wedge having at least one inclined surface inclined from the vertical at an angle from about 0.25xc2x0 to about 30xc2x0, so as to form a wedge cavity; whereby the wedge is releasably insertable in the wedge cavity and the tool, however formed, is releasably insertable in the tool cavity.
It is a specific object of this invention to cut, using wire EDM, not only the wedge, but also the tool-and-wedge cavity from the retainer block using a thin wire having a sufficiently small diameter to provide the desired clearances between tool, wedge and cavity.